1. Field of the Invention
The present invention relates to vibrating gyroscopes, and more particularly, to a vibrating gyroscope used to an image stabilizer in, for example, a digital still camera and a digital video camera.
2. Description of the Related Art
FIG. 18 is a perspective view illustrating an example of a known vibrating gyroscope. The vibrating gyroscope 1 includes a tuning-fork vibrator 2. The vibrator 2 includes a base 2a and two legs 2b and 2b that extend from the base 2a. The vibrator 2 includes two tuning-fork-shaped piezoelectric substrates 3a and 3b that are laminated on each other. The laminated piezoelectric substrates 3a and 3b are polarized in opposite directions along the thickness thereof. An intermediate metal layer 4 is interposed between the piezoelectric substrates 3a and 3b. In addition, drive electrodes 5a, 5b, and 5c are provided on a principal surface of the piezoelectric substrate 3a. The three drive electrodes 5a, 5b, and 5c are separated from each other in a width direction of the piezoelectric substrate 3a. More specifically, the drive electrodes 5a, 5b, and 5c are separated from each other by separating portions that extend in the longitudinal direction of the legs 2b and 2b. In addition, detection electrodes 6a and 6b are provided on a principal surface of the other piezoelectric substrate 3b. The two detection electrodes 6a and 6b are separated from each other at a central portion of the piezoelectric substrate 3b in the width direction thereof.
The vibrator 2 is attached to a support plate 7. The support plate 7 has, for example, a substantially rectangular plate shape, and the base 2a of the vibrator 2 is adhered to a central portion of the support plate 7. The support plate 7 includes supporting rods 8 at locations spaced from a portion at which the base 2a is adhered toward the ends of the support plate 7. The supporting rods 8 are arranged so as to extend from end portions of the support plate 7 along the legs 2b and 2b of the vibrator 2. The vibrator 2 is fixed to a case or other suitable structure by the supporting rods 8.
In the vibrating gyroscope 1, an oscillator circuit is connected between the middle drive electrode 5b and the drive electrodes 5a and 5c disposed on either side of the middle drive electrode 5b. The oscillator circuit includes, for example, an amplifier circuit and a phase compensator circuit. The detection electrodes 6a and 6b are connected to a detection circuit. The detection circuit includes a differential circuit, a synchronous detection circuit, an integrator circuit, a direct-current amplifier circuit, etc.
The oscillator circuit applies an electric field to the vibrator 2 in a direction substantially perpendicular to the direction of polarization, so that the legs 2b and 2b of the vibrator 2 vibrate so as to move toward and away from each other. In this fundamental vibration, the two legs 2b and 2b vibrate in the same manner with respect to the direction of polarization, and accordingly, the detection electrodes 6a and 6b output the same signal. Therefore, no signal is output from the differential circuit in the detection circuit. In this state, when a rotational angular velocity about a central axis of the vibrating gyroscope 1 is applied, a Coriolis force is applied to the legs 2b and 2b along an axis substantially perpendicular to the direction of fundamental vibration. The Coriolis force is applied to the legs 2b and 2b in opposite directions, and accordingly, the two legs 2b and 2b move in opposite directions. Due to the displacements of the legs 2b and 2b, the detection electrodes 6a and 6b output signals in opposite phases and a large signal is output from the differential circuit.
The output signal from the differential circuit is detected by the synchronous detection circuit in synchronization with a signal from the oscillator circuit, and is converted into a direct-current signal by the integrator circuit. Then, the output signal from the integrator circuit is amplified by the direct-current amplifier circuit. Accordingly, the magnitude of the rotational angular velocity can be determined based on the magnitude of the output signal from the direct-current amplifier circuit. In addition, the direction of the rotational angular velocity can be determined based on the polarity of the output signal from the direct-current amplifier circuit.
In this vibrating gyroscope 1, when a rotational angular velocity is applied, the two legs 2b and 2b of the vibrator 2 generate torsional vibration in which the fundamental vibration and vibration substantially perpendicular thereto that is caused by the Coriolis force are combined. The torsional vibration of the vibrator 2 generates two node lines on the support plate 7. More specifically, due to the torsional vibration of the vibrator 2, the support plate 7 generates a bending vibration having a torsional center at a joining portion to which the vibrator 2 is adhered. The two node lines of the bending vibration of the support plate 7 appear at locations outside the vibrator 2. Accordingly, the supporting rods 8 are formed on the two node lines of the bending vibration of the support plate 7, so that the bending vibration of the support plate 7 is not impeded and the vibration of the vibrator 2 is also not impeded when a rotational angular velocity is applied. As a result, an accurate signal corresponding to the rotational angular velocity can be obtained by the vibrating gyroscope 1 (see Japanese Unexamined Patent Application Publication No. 2000-292171).
In such a vibrating gyroscope, the support plate is supported by the supporting rods provided at locations outside the portion at which the vibrator is adhered. Therefore, even though the support plate is supported at the node lines of the bending vibration of the support plate, the support plate cannot freely bend and the torsional vibration of the vibrator cannot be completely prevented from being impeded in the process of detecting the rotational angular velocity. As a result, the vibration frequency of the vibrator is shifted and resonance in a vibration mode different from the expected vibrating mode becomes significant, whereby it is difficult to detect an accurate rotational angular velocity. In addition, since the support plate must extend to regions around the two node lines of the bending vibration, the overall size of the vibrating gyroscope is relatively large.